TRANSDIFFERENTIATION OF OUTGROWTH CELLS AND CULTURED EPITHELIAL-CELLSFROM SWINE TRACHEA

The morphologic and functional properties of explant out-growth cells and epithelial cells isolated from swine trachea epithelium by proteol ysis were examined. A mixed population of ciliated, serous, and basal cells, obtained from outgrowths, from proteolysis of trachea epitheliu m, and from unattached explants in organ culture, all yielded cell cul tures that were composed almost entirely of mucus-secreting cells. Whe n the cells were grown in primary or secondary culture on a modified c ollagen matrix in supplemented HAM:DMEM (1:1) medium they expressed a mucus-secreting phenotype with numerous mucus granules at various stag es of maturation and incorporated [H-3]GlcN and (SO4)-S-35 into secret ed mucin glycoproteins. Results obtained in these studies suggest that extensive transdifferentiation of ciliated and serous cells to mucus- secreting cells occurs after the release and during subsequent attachm ent and culture. Ciliated cells containing mucus granules were seen in various stages of cilia resorption. Basal cells containing mucus gran ules were also frequently observed. The number of mucus-secreting cell s and the synthesis of mucin glycoproteins increased dramatically with time of attachment and culture, whereas cell proliferation, populatio n doubling time of 72 h, and incorporation of [H-3]-thymidine into DNA increased much more slowly. The number of mucus-secreting cells corre lated closely with the level of secretion of mucin glycoproteins. Take n collectively, these studies help to elucidate the transdifferentiati on process, which dramatically increases the number of mucus-secreting cells after disruption and release of epithelial cells from swine tra cheobronchial epithelium. A similar mechanism involving disruption of the extracellular matrix may be involved in the stimulation of hyperse cretion of mucus and mucin glycoproteins by chemical and infections ir ritants.